Torque converters are well known in the art. Torque converters often include a piston that is axially moveable for engaging a clutch. Leaf springs may be included for transferring torque (directly or indirectly) from the cover of the torque converter to the piston. The leaf springs enable the transfer of torque through the leaf springs to the piston while also being able to flex to enable the piston to move axially with respect to the torque converter cover or a drive plate for the leaf springs. For example of one type of leaf spring arrangement, see United States Patent Publication No. 2008/0190723 (Heck et al.) which Patent Publication is hereby incorporated by reference in its entirety. Typically, the leaf springs are arranged so that in a normal drive mode of operation of the torque converter, the leaf springs are subjected to only tensile forces. Since the springs are, for example, thin plate-like members, they have good tensile strength.
While coasting in an automobile, however, the forces are reversed so that the leaf springs are subjected to compression forces. By coasting, it is meant generally that the engine is idling, but the vehicle is moving, including the components of the torque converter. The compression forces on the leaf springs are a result of resistance of the engine that is coupled to the torque converter. The compression forces create a risk that the leaf springs will buckle, and become permanently bent or deformed. The engine resistance is sometimes referred to as providing “engine braking” Basically, the torque converter and other elements are still rotating when the automobile is coasting, but the engine is not (or only to some marginal degree while idling), so the torque converter components generally act to rotate the engine while the engine is idling, instead of the other way around. The engines of many automobiles, such as typical passenger cars, do not usually exhibit engine resistance large enough to make buckling of the leaf springs a substantial risk. However, the engines of some automobiles, such as semitrailers, are arranged to strongly resist rotation while coasting, and provide a large amount of engine braking, which is exerted as compression forces on opposite ends of the leaf springs. As a result, in these vehicles there is a very real risk that the leaf springs will buckle when coasting.